1. Field of the Invention
The present invention is directed to valves for the control of the flow of molten material from a vessel, and more particularly such valves as exemplified in Shapland U.S. Pat. No. 3,352,465 reissued as U.S. Pat. No. Re. 27,237 and Shapland and Shapland U.S. Pat. No. 4,063,668 and Shapland U.S. Pat. No. 4,314,659. In both of these devices pressure is applied to opposed refractory plates in the valve which can permit teeming or shutting the same off or indeed throttling depending upon the mode of operation desired.
2. The Prior Art
Attempts have been made for one hundred years or more to develop an external device to control the flow of molten material from a vessel. One of the earliest devices is disclosed in the Lewis U.S. Pat. No. 311,902 issued in 1885. A number of improvements of this device have been patented over the years but none of them was commercially successful until in the 1960's. Then the need to hold molten metal in a vessel for longer periods and the need to teem for longer periods was brought on by the advent of the continuous casting of steel. At that time, the Interstop valve based on the Lewis patent and the Flo-Con Systems, Inc. valve based on the Shapland U.S. Pat. No. 3,352,465 (re-issued as U.S. Pat. No. Re. 27,237) utilizing valve plate yieldable edge support through first class, spring forced levers were used for such control. Since that time, others have entered the field and a number of improvement patents relate to the means of attaching the devices to the vessel to allow easier service or alternate methods for applying the sealing pressure. Significant of the later of these is the Grosko and Shapland U.S. Pat. No. 3,604,603 showing fluid pressure enclosing tubes located under the edges parallel to travel of a sliding plate and Shapland and Shapland U.S. Pat. No. 4,063,668 which discloses a sliding plate supported by a plurality of pressure devices distributed under the plate. Physical limitations on the location of these pressure devices prevent obtaining uniform pressure over the entire sliding plate surface. Mechanical spring devices are subject to loss of force at high temperature and sealed pressure units used in place of mechanical springs may result in excessive sealing forces at elevated temperatures. Uncontrolled sealing forces may result in high sliding force requirements and make opening and closing of the device for refractory replacement difficult.